The present invention relates to a combustion chamber for gas turbines.
As is known, gas turbines are machines which consist of a compressor and of a turbine with one or more stages, wherein these components are connected to one another by a rotary shaft, and wherein a combustion chamber is provided between the compressor and the turbine.
In order to pressurise the compressor, it is supplied with air obtained from the external environment.
The compressed air passes through a series of pre-mixing chambers, which end in a nozzle or a converging portion, into each of which an injector supplies fuel which is mixed with the air, in order to form an air-fuel mixture to be burnt.
By means of one or more burners, supplied by a pressure network, there is admitted into the combustion chamber the fuel which is necessary in order to produce the combustion, which is designed to give rise to an increase in the temperature and enthalpy of the gas.
The known burners have a complex structure, inside which there is also present an injector for the liquid fuel, which in turn is contained inside an appropriately converging body, which in common technical language is generally known as the shroud, and is connected to a corresponding coupling, which permits connection to the combustion chamber.
Suitable turbulence in the flow of compressed air obtained from the compressor is created downstream of the injector, by associating with each burner an element which according to the art is generally known as the swirler, which intercepts the flow of air obtained from the compressor, and has a complex shape consisting of two series of blades oriented in opposite directions, all of which is designed to produce this turbulence.
The turbulence thus created makes it possible inter alia to mix the air itself satisfactorily with the fuel in the combustion chamber.
In order to improve the characteristics of stability of the flame, in the case of use of gaseous fuel, there is also generally provided a parallel fuel supply system, which can generate pilot flames in the vicinity of the output of the burner.
Finally, via corresponding ducts, the high-temperature, high-pressure gas reaches the various stages of the turbine, which transforms the enthalpy of the gas into mechanical energy which is available to a user.
If the area in which the combustion takes place is observed in greater detail, it can be seen that typically, the fuel is burnt in a combustion chamber which is delimited by what is generally known according to the art as an outer liner and an inner liner.
The inner liner is concentric relative to the outer liner, and co-operates with the latter such as to define an annular space which constitutes the actual combustion chamber.
As is known, in the design of combustion chambers for gas turbines, prevalence is given to considerations of stability of the flame and control of the excess air, in order to create the ideal conditions for combustion.
A second factor which affects the design of the combustion chambers of gas turbines is the tendency to make the combustion take place as much as possible in the vicinity of the dome of the combustion chamber.
Thus, in order to protect the combustion chamber against the high temperatures which exist during the combustion, it is known to provide a shield in the vicinity of the output of the burner.
However, owing to the high temperatures which the shield must withstand, it is necessary to provide a structure which can disperse the heat efficiently.
A known structure for shields of this type comprises a pair of metal plate parts, which are adjacent to one another and are separated by a plurality of contact elements, such as to define inner spaces which can permit good dispersion of heat.
However, it is known that although this structure fulfils satisfactorily its own technical function, it has a complex shape, consisting of several component parts, which must be assembled to one another.
The object of the present invention is thus to provide a combustion chamber for gas turbines, which has shields which are produced simply and inexpensively, whilst being able to provide the required properties of protection against the heat of the flame.
Another object of the invention is to provide a combustion chamber for gas turbines, which can be produced at a low cost, and has a reduced number of component parts.
A further object of the invention is to provide a combustion chamber for gas turbines, which does not require costly modifications to the design of the conventional chambers.
This object and others are achieved by a combustion chamber for gas turbines, comprising an inner liner and an outer liner, wherein the inner liner is substantially concentric relative to the outer liner, such as to define an annular inner space, and wherein a shield is provided at the output of each of the burners, characterised in that each of the said shields comprises a single metal plate part, and in that at least one of the said liners has a plurality of holes, in sections adjacent to the longitudinal development of the said shield.
More particularly, in the combustion chamber for gas turbines according to the present invention, both the outer liner and the inner liner have a plurality of holes, in sections adjacent to the longitudinal development of the shield, such as to define corresponding gaps for circulation of air.
According to a preferred embodiment of the present invention, each of the shields consists of a body which has an upper wall, disposed adjacent to the drilled portion of the outer liner, and a lower wall, disposed adjacent to the drilled portion of the inner liner.
The upper wall of each shield is slightly convex, and has a surface which is larger than the corresponding lower wall of the shield, which in turn is slightly concave.
In addition, each shield is provided with a substantially cylindrical portion, which has a diameter slightly larger than the diameter of a corresponding raised portion for the converging output end of the corresponding burner, such as to assist perfect connection between these elements.
According to another preferred embodiment of the present invention, each shield has a plurality of projections, which are disposed both on the upper wall and on the lower wall, and can come into contact respectively with the outer liner and with the inner liner.
According to another preferred embodiment of the present invention, a substantially annular dome is provided in the upstream part of the combustion chamber, where it has a plurality of apertures, each of which is provided with a raised portion for the converging end of the corresponding burner.
In addition, the surface of the dome has a plurality of through holes, in order to increase the circulation of air on the shield.
Finally, each shield has a front wall, which connects the upper wall and the lower wall of the shield, and is adjacent to the drilled surface of the dome.
The combustion chamber for gas turbines according to the present invention makes it possible firstly to protect the dome, and the sections of the outer and inner liners which are most affected by the effects of the combustion, whilst avoiding excessive heating of the shield.
This result is obtained at extremely low costs, since the shield itself is produced in an extremely simple manner, by means of a single metal plate part.
In addition, in order to produce ducts for circulation of cooling air for the shield, it is sufficient to provide a plurality of holes along the surfaces of the inner liner and the outer liner, which operation clearly does not required particular additional costs.
Further characteristics of the invention are defined in the claims attached to the present patent application.